This invention relates generally to a process for making methylaluminoxanes and more specifically to the preparation of methylaluminoxanes from higher alkylaluminoxanes by a catalyzed, alkyl-group-exchange reaction.
Hydrocarbylaluminoxanes, including methylaluminoxanes complexed with transition metal compounds, have been found to be very effective olefin polymerization catalysts (Manzik et al. U.S. Pat. No. 3,242,099). Hydrocarbylaluminoxanes can be made by the controlled partial hydrolysis of hydrocarbyl aluminum compounds and methylaluminoxanes have been prepared in this manner. However, this requires the preparation and purification of trimethylaluminum. Higher alkylaluminoxanes and especially ethylaluminoxanes are easier to prepare on a commercial scale. I have found that methylaluminoxanes can be prepared by reacting a higher alkylaluminoxane with a methylhalide so as to exchange the methyl group for the higher alkyl group. Such exchanges have been used to prepare trimethylaluminum from triethylaluminum as disclosed in U.S. Pat. No. 4,364,872 using a bismuth based catalyst; but the effect of using such catalysts with aluminoxanes, which are complex compounds containing the ##STR1## unit, where R is an alkyl group and n is about 1-20, and which can be linear or cyclic compounds, could not be predicted.